1. Technical Field
Exemplary embodiments of the inventive concept relate to a semiconductor device, and more particularly to a semiconductor device capable of testing a transmission line for an impedance calibration code.
2. Discussion of Related Art
When a signal is transmitted through two transmission lines having different impedances from each other, a part of the transmitted signal may be lost. Further, the amount of signal loss may increase as the speed of signal transmission increases. Therefore, in a semiconductor device that transmits a signal at a high speed through a transmission line, the impedance of an internal transmission line should be matched with the impedance of an external transmission line.
A semiconductor device that transmits signals at high speeds through transmission lines may include an off-chip driver (OCD) and an on-die-termination circuit (ODT) for impedance matching with an external transmission line. An OCD may perform an impedance matching operation to transmit the signal without loss when the signal is output from the semiconductor device to the exterior. An ODT may perform an impedance matching operation to transmit the signal without loss when the signal is input from the exterior to the semiconductor device. Therefore, the OCD/ODT pair may prevent reflection of an transmitted signal.
An impedance characteristic of the OCD or the ODT may be calibrated to obtain a higher degree of signal integrity. The need for impedance calibration increases as the speed of signal transmission increases. A semiconductor device may include an impedance calibrating circuit to calibrate impedance of an ODT or an OCD using an external reference resistor. The impedance calibrating circuit may perform the impedance calibration of the OCD and the ODT by adjusting the magnitude of the impedance of the reference resistor.
As the number of signals input or output to or from a semiconductor device increases, so does the number of input pads and input/output pads that are provided in the semiconductor device. Each of the input pads may be connected with a corresponding ODT and each of the input/output pads may be connected with both a corresponding OCD and a corresponding ODT. Due to the increase in the number of pads, it is difficult to limit an arrangement of the pads to some specific area of the semiconductor device. Thus, the pads may be arranged in different areas of the semiconductor device along with a corresponding OCD and ODT.
An impedance calibrating circuit may use code transmitting lines to transmit a calibration code to the OCDs and ODTs that are arranged in the different areas of the semiconductor device. However, the calibration code may have been transmitted with a distortion, or a line cut or short may be present in one of the code transmitting lines.